This invention relates to a method for making a model for a dental prosthesis for mounting in a dental foundation member such as an implant having an internal hex, the implant being embedded in a jawbone of a patient, and a dental formation mounting arrangement for use in such a method.
After a period of, for example, three to six months, has been allowed for an implant in the jawbone of a patient to settle, it is usual for an impression to be made in a plastic material of the surfaces of at least part of the gum, and any adjacent teeth that surround the embedded implant. The impression is then used to make a model of that part of the gum and the adjacent teeth. A dental technician uses the model to make a dental prosthesis, which may be in the form of a false tooth, for fitting into a socket in the implant.
An integrated implant prosthesis must fit accurately and be designed to optimise stress distribution to the supporting bone. It is therefore essential for this prosthetic restoration of an implant that the position of each implant in a jaw bone be accurately recorded and transferred to the model. This is particularly important for a screw retained prosthesis.
In practice, relative orientation of the implant to the desired orientation of the dental prosthesis it is to support is unpredictable, both because the actual location of the settled implant is difficult to predict and because the dental surgeon may have to overcome one or more of a number of problems when implanting the implant which means that the orientation of the implant may differ from the optimum.
WO93/20774 discloses a dental formation mounting arrangement comprising a locating element which is adapted to be engaged in a socket formed in a dental foundation member on which the dental formation is to be mounted so as to be held against rotation relative to the dental foundation member and fixing means for fixing the locating element to the foundation member when the locating element is so engaged in the socket, wherein the dental formation mounting arrangement comprises a locating bush which is to be fitted over the locating element, when the latter is engaged in the socket and which is to carry said dental formation.
W093/20774 further discloses a method of making a model of at least part of the gum utilising the dental formation mounting arrangement described above. The arrangement is described as comprising essentially three components and, due to the configuration of the components, requires the use of a non-standard impression tray which is specific to the mounting arrangement.
W096/29019 discloses a dental formation mounting arrangement including an anchor pin or post with an elastic clamp head which is screwed into a tapped hole in an implant which is implanted in the jawbone of a patient, and a contoured element which is snap-fitted onto the anchor pin. The contoured element may be an impression cap or tray, a crown cap or a secondary pin or post. The snap-fitting comprises an annular shoulder which is formed internally on the contoured element and which engages the elastic clamp head in a snap-fit manner. The relative orientation of the contoured element to the implement is imprecise because the anchor pin or post is screwed into the implant and the contoured element can be fitted onto it at random.
According to one aspect of this invention there is provided a dental formation mounting arrangement including a locating element having a portion which is formed so as to be a snug fit in a socket formed in a dental foundation member on which a dental formation is to be mounted, fixing means for fixing the locating element to the foundation member when the locating element portion is fitted into the socket, and a mating element attachable to and detachable from the locating element by means which provide a snap-fit attachment, wherein said locating element has a flat surface which is adapted to make face to face contact with a corresponding flat surface of the socket when that locating element portion is fitted into the socket whereby to hold the locating element against rotation relative to the dental foundation member and each of the locating and mating elements is provided with a respective formation, the formations on the locating and mating elements being adapted to be positively interengaged when the mating element is snap-fitted onto the locating element and the mating element is in a certain orientation relative to said flat surface.
Preferably the mating element is a hollow body provided with apertures in its structure which place its interior in communication with its surrounds, the arrangement being such that, when the mating element is embedded in dental impression material during a process of making a dental impression, such dental impression material can extend through the apertures and form structural links between such dental impression material within the interior of the hollow body and such dental impression material that surrounds the hollow body. The means for providing a snap-fit may comprise at least one locating member which protrudes from one of the locating and mating elements, the at least one locating member being locatable in a corresponding recess formed in the other of the locating and mating elements, the at least one locating member and the corresponding recess serving as the formations. The at least one locating member may comprise one or more locating pins and may protrude from the locating element and be locatable in a respective slot in the mating element.
In another embodiment the locating and mating elements are adapted to be snap-fitted together by pushing a projecting portion of one of them into a cavity formed in the other and the formations include a wall which extends partway around the mouth of the cavity and which seats substantially without clearance in a corresponding recess formed in the one of the locating and mating elements, movement of the other element relative to the one element in the direction that would displace the wall around the periphery of the cavity being stopped by abutment with the ends of the recess in which the wall seats without substantial clearance.
Conveniently the locating element is formed from metal and the mating element is formed from a plastics material. The mating element may include at least one flange which is embedable in a dental impression material in use, enabling the mating element to be removed with the impression material once the impression material has set.
According to another aspect of this invention there is provided a method for making a model of at least part of the gum and one or more adjacent teeth that surround one or more dental foundation members embedded in the jawbone of a patient, said one or more dental foundation members each having a receiving socket therein, the method including the steps of:
(i) locating a locating element in the socket of the or each dental foundation member;
(ii) attaching a mating element to the locating element by means of a snap-fit;
(iii) placing a dental impression tray filled with dental impression material around the teeth, gums and the or each dental foundation member;
(iv) removing the impression tray and dental impression material with the mating element embedded therein from the mouth of the patient by overcoming the snap-fit holding the mating element on the locating element once the dental impression material has set; and
(vii) forming a replica of the teeth and gums of the patient using the impression created in the dental impression material once set, as a maul; wherein the method also includes
(viii) providing the socket and a portion of the locating element which is located in the socket with mating flat faces which make face to face contact with one another when the locating element is located in the socket whereby the locating element is held against rotation relative to the dental foundation member; and
(ix) positively interengaging certain formations provided on the locating and mating elements so that the mating element is in a certain orientation relative to said dental formation member.
Preferably the method includes the step of selecting a hollow body as the mating element, the hollow body having apertures in its structure which place its interior in communication with its surrounds and, filling the interior with dental impression material so that it extends through the apertures and forms structural links between the dental impression material within the hollow body and the dental impression material that surrounds the body in the tray.